The present invention relates generally to the packaging of integrated circuits in leadframe based microarray packages.
There are a number of conventional arrangements for packaging integrated circuits. Many packaging techniques use a leadframe that has been stamped or etched from a metal (typically copper) sheet to provide electrical interconnects to external devices. One relatively recently developed packaging style, which is sometimes referred to as a leadframe based microarray package is generally illustrated in FIG. 1. In a microarray package, the leadframe typically includes an array of contact posts 22 that are exposed on the bottom surface of the package and lead traces 24 that may or may not be exposed at the bottom surface of the package. A die mounted on the lead frame is wire bonded (or otherwise electrically connected) to the lead traces, which serve as electrical connectors between the bonding wires and the contact posts 22. Often the microarray package will also have a die support structure 26 that supports the die.
Microarray packages have a number of potential advantages. For example, they are relatively low cost, they may be configured to be pin compatible with conventional BGA packages and they allow a relatively large number of contacts for a given package size. Also, since the lead traces permit “routing” of signals to contact pads located under the die, a package with a relatively smaller footprint may be used for a given die size and pin count as compared to many other leadframe based packages.
As the capacity of these microarray packages increases, the number of contact posts in the array of contact posts likewise multiplies. Consequently, when the microarray packages increase in size, the outermost contact posts (e.g., 22A) are positioned further and further away from a center of the package (e.g., 22B). Hence, due to the geometry and position of the outermost contact posts, the shear and stress levels experienced at these outermost contacts due in-part to operational board level thermo-cycling is significantly more than that experienced at the contact more central to the microarray package. Accordingly, contact failure at such outermost contact interfaces is more prevalent.
Given their many advantages, microarray packages in general have recently generated a great deal of interest within the semiconductor industry. Although existing techniques for fabricating microarray leadframes and for packaging integrated circuits using microarray leadframe technology work well, there are continuing efforts to develop even more efficient designs and methods for packaging integrated circuits using microarray leadframe technology.